Head Space

[purple bikerr]

Hey all!! First time poster here. I am an experienced reloader, been doing it for 28 yrs. Rifle and hand gun. But this will be my first rodeo loading for a semi auto rifle. I just bought my 1st AR. What is the proper headspace on a .556? Yes I am sure it will safely shoot .556 ammo. It's a Spikes ST-15.

I found on the 'net that max is 1.464, but the Winnie factory ammo I had measured 1.458.

So what do I set my sizing die to?

I know that I cannot "bump" the shoulder back .002" like I do for my bolt guns. .002" is not enough to reliably cycle the bolt (action) on a semi auto. Is this gonna be a "trial and error" exercise to find the proper headspace for "my" gun?

This is the first question I have concerning AR's. Many more to come.

Edit: I just measured my fired brass and they head spaced at 1.462". Reading this post again I think I answered my own question. Seems 1.458 is the magic number.